Antiseismic support

ABSTRACT

The present invention concerns an anti-seismic support for supporting a construction engineering structure, which comprises a support ( 14 ) having a concave sliding surface ( 17 ) and a sliding block ( 16 ) with a convex sliding surface ( 16 d) in sliding contact with the concave sliding surface ( 17 ), the sliding block ( 16 ) being capable of sliding with pendulum motion relative to the concave surface ( 17 ) in response to an earthquake tremor or shock, the device ( 11 ) comprising a sliding material ( 19 ) between the concave sliding surface ( 17 ) and the convex sliding surface ( 16   b ), where the friction coefficient between the sliding surfaces ( 16   b,    17 ) is above 10% when the device ( 11 ) is loaded with a pressure above 30 MPa and the sliding surfaces are caused to slide at a sliding speed of more than 50 mm/s at a temperature of 20° C. or more.

The present invention relates to an antiseismic support for supportingcivil or construction engineering structures, namely including bridges.

Either term “civil engineering structure” or “construction engineeringstructure” is used herein to designate civil engineering structures suchas buildings or bridges, but also silos and tanks.

Antiseismic support devices are known in the art, which are designed tobe installed between the foundation of a civil engineering structure(such as a building or a bridge) and the structure itself, to protect itfrom an earthquake tremor or shock.

“Pendulum” devices, like the one known from U.S. Pat. No. 4,644,714, areamong the devices that accomplish this task: this anti-seismic supportcomprises a lower support and an upper support, which are joined to thestructure to be supported and the foundations of the structurerespectively.

Both supports have a respective concave sliding surface and areseparated from each other by a slider. The slider has two convexsurfaces mating and in contact with the concave surfaces of the upperand lower supports, to form a ball joint.

In the event of an earthquake tremor or shock, the slider can slide witha pendulum motion relative to the first support, thereby protecting theoverlying structure from the effects of the earthquake.

The sliding surface of the slider in contact with the concave slidingsurface of the first support is usually coated with a sliding materialto facilitate mutual sliding of the surfaces.

As is known in the art, a composite material comprising PTFE with carbonfibers or glass fibers is used as a sliding material. The slidingmaterial has a high friction coefficient, up to 20%, which allowdissipation of a large amount of energy during rocking, following anearthquake tremor or shock.

Nevertheless, these devices do not have an adequate wear resistance andfor this reason are not suitable for use in supporting structures (suchas bridges) that are subject to continuous and frequent in-servicemovements even when no earthquake occurs, e.g. due to thermal expansion,wind action, or to a sudden change of the load supported by thestructure.

In another prior art, according to EP 1 836 404, pendulum anti-seismicbearing devices have been provided, which use a different type ofsliding material.

Particularly, according to EP 1 836 404, the sliding material may beunfilled hard PTFE or UHMWPE. These materials exhibit a high wearresistance, and a relatively low friction coefficient, which allows themto accommodate the in-service movements of structure, but prevents themfrom dissipating large amounts of energy, as might be required in thecase of a high intensity earthquake.

In order to use the devices as disclosed in EP 1 836 404 in highlyseismic areas, it was proposed to apply viscous dampers to the devices,for dissipating the high energy developed in the event of a strongearthquake shock. This increases the dimensions and costs of the device,due to the parts required in addition to those conventionally used inthis kind of supports.

A further drawback of prior art sliding materials is their fastmechanical degradation due to the heat dissipated during the earthquake:at high slip velocities, such as those generated by a high-intensityearthquakes, high friction coefficient and extended seismic excitation,the relative sliding motion of the slider surfaces generates hugeamounts of heat, causing fast degradation of the properties of thesliding material.

Therefore, it would be desirable to provide an anti-seismic support thatis less exposed to degradation caused by the heat generated by thesliding movement of the slider, while still allowing heat generation byfriction, i.e. dissipation of the energy transmitted by the earthquaketo the structure.

In the light of the above prior art, the object of the present inventionis to provide an anti-seismic support that can solve the above mentionedprior art drawbacks.

Particularly, one object of the invention is to provide an anti-seismicsupport that can be used to support bridges, e.g. road or railroadbridges, and can withstand high-intensity and long-lasting earthquakes.

A further object of the invention is to provide an anti-seismic supportthat is not too large, has a simple structure with a small number ofparts and is reliable with time.

According to the present invention, these objects are fulfilled by adevice as defined in claim 1.

The features and advantages of the present invention will become moreapparent from the following detailed description of one practicalembodiment, which is given as a non-limiting example with reference tothe annexed drawings, in which:

FIG. 1 shows a sectional view of an anti-seismic support of theinvention;

FIG. 2 shows an enlargement of the sectional view of FIG. 1.

FIG. 1 shows an anti-seismic support 11 which is designed to beinstalled among the foundations 13 of a construction engineeringstructure, and the construction engineering structure 12 itself.

The anti-seismic support 11 is used to support the constructionengineering structure and protect it in the event of an earthquake.

The construction engineering structure 12 may be a bridge, e.g. a roador railroad bridge. Nevertheless, the bearing device 11 may be alsoemployed to support buildings or other constructions, such as silos andtanks.

The anti-seismic support 11 comprises an upper support 14 (or firstsupport 14) having a concave sliding surface 17, and a sliding block 16in sliding contact with the sliding surface 17.

The sliding block 16 has a convex sliding surface 16 b, which contactsthe concave sliding surface 17 of the upper support 14.

The sliding block 16 further comprises a convex joint surface 20, facingaway from the convex sliding surface 16 b, which is adapted to contact acorresponding concave joint surface 21, formed in a second support 15.

In the figures, the second support 15 is located below the sliding block16 and will be mentioned hereinbelow as “lower support 15”.

Thus, the anti-seismic support 11 actually comprises two supports 15,14, which are separated by the sliding block 16. An articulation jointis formed between the sliding block and one of the two supports 15, 14(15 in FIG. 1), and a slip joint is formed between the sliding block 16and the other of the two supports (14 in FIG. 1), to absorbearthquake-induced movements.

Obviously, while reference is expressly made in the drawings and thedescription to a single configuration (with the articulation joint belowthe sliding surface), the kinematically opposite configuration (with thearticulation joint above the sliding surface) is possible andtechnically equivalent, and shall be deemed to be implicitly disclosedherein.

Likewise, the configuration as shown in FIGS. 2 a and 2 b of patent EP 1806 404, in which the pendulum anti-seismic support comprises two slipinterfaces, instead of a slip interface and an articulation joint, isalso deemed to be incorporated herein by reference.

Therefore, if the anti-seismic support comprises two slip interfaces,the considerations relating to the slip interface of the presentinvention shall be deemed to be equally applicable to both interfaces ofthe anti-seismic support.

Preferably, the convex sliding surface 16 b and the concave slidingsurface 17 have mating curvatures, to allow a pendulum motion of thiskind of devices 11; for instance, they may have a spherical shape andhence have the same radius of curvature; alternatively, otherconfigurations may be envisaged, in which at least one of the twosurfaces has a variable radius of curvature, for improved centering ofthe sliding block 16.

The upper support 14 is preferably in the form of a plate and ispreferably integrally joined, by known fastening means, to aconstruction engineering structure to be supported. The upper support 14is preferably made of steel, but may be also made of aluminum or anothermaterial.

During an earthquake tremor or shock, the sliding block 16 is adapted toslide along the concave sliding surface 17 with a pendulum motion.

In the figures, the sliding block 16 is shown in its equilibriumposition, i.e. centered relative to the concave sliding surface 17. Thesliding block 16 is in this equilibrium position before the earthquakeand, depending on the interaction of certain factors, including the typeof earthquake, it can recover it at the end of the earthquake.

The bearing device 11 comprises a sliding material 19 that forms theconcave sliding surface 17 of the upper support 14 or the convex slidingsurface 16 b of the sliding block 16.

Advantageously, the sliding material 19 may be applied to the slidingblock 16 or the upper support 14 and may be placed in a matingly shapedseat formed in the sliding block 16 or the upper support 14.Advantageously, the sliding material has a thickness (e.g. a constantthickness) greater than the depth (e.g. a constant depth) of the seat inwhich it is embedded, thereby projecting out of it.

Alternatively, the sliding material 19 may be applied to the slidingblock 16 or the upper support 14 using adhesives or mechanical fastenermeans, such as screws and/or rivets; in this case, the seat may beomitted.

Preferably, the sliding material 19 is applied to the sliding block 16and forms the convex sliding surface 16 b of the sliding block 16. Thesliding material 19 may be in the form of a sheet of material, e.g.having the thickness of a few millimeters.

The sliding material 19 may include a polymeric material with apolymeric, synthetic, ceramic or metal filler, carbon fiber or glassfiber fillers being excluded from such alternatives.

The sliding material 19 has a relatively high friction coefficient atvelocities higher than those typically associated with in-servicemovements, e.g. movements that displace the elements fixed to theanti-seismic support 11 due to thermal expansion, wind action orvariable loads acting upon the surface, or to viscous shrinkage ofconcrete. The concave sliding surface 17 of the upper support 14 and theconvex sliding surface 16 b of the sliding block 16 may slide one uponthe other with 9% friction or more, or preferably 10% friction or more,if the device 11 has such a load thereon that an average pressure(defined as the ratio of the vertical load on the device to theprojection area on a flat surface of the curved contact surface of theconvex sliding surface 16 b of the sliding block 16 and the concavesliding surface 17 of the upper support 14), of 30 MPa exists betweenthe surfaces, with a mutual sliding velocity of 50 mm/s or more.

Therefore, the bearing device 11 is adapted to dissipate a large amountof energy, due to its high friction in case of relatively high slipvelocities, similar to those occurring in the event of a high-intensityearthquake.

Furthermore, the sliding material has a high thermal conductivity, of0.50 W/m*K or more.

This relatively high thermal conductivity value allows fast removal ofheat from the contact surface of the sliding block 16 and the uppersupport 14. In fact, the earthquake energy is dissipated and convertedinto thermal energy at the interface between the convex sliding surface16 b of the sliding block 16 and the concave sliding surface 17 of theupper support 14. In the polymer materials that are typically used as asliding material 19 in the prior art, thermal conductivity is much lowerthan 0.50 W/m*K. This prevented efficient removal of heat from thecontact surface and created peak temperatures in the sliding material19, possibly degrading the mechanical properties of the material. Thesedegradation effects may include softening of the sliding material 19,which affects its load withstanding capacity and/or reduction of thefriction coefficient of the polymer material, leading to a reducedearthquake energy dissipation capacity and reduced performances of theanti-seismic support.

The sliding material 19 as used in this invention is adapted to supporthigh heat generation on the sliding surfaces as compared with prior artmaterials.

In the case of the present invention, the seismic isolation device ischaracterized in that it uses, as a sliding material 19, a materialhaving a high thermal conductivity, which allows temperature increase tobe limited at the convex sliding surface 16 b of the sliding block 16and the concave sliding surface 17 of the upper support 14.

Preferably, the thermal conductivity of the sliding material is higherthan 0.60 W/m*K, more preferably higher than 0.70 W/m*K, and or lowerthan 0.90 W/m*K.

The sliding material 19 that is used in the device 11 also has a highwear resistance.

Particularly, the properties of the sliding materials 19 typicallyundergo the wear test as set forth in EN 15129:2009 for buildings,Paragraph 8.3.1.2.5 and or the US standard “AASHTO LRFD Bridge DesignSpecification”, Paragraph 15.10.1.2.

Therefore, the anti-seismic device 11 is adapted to also withstandlow-velocity movements, such as those that may occur when the device 11is installed in a structure that is required to accommodatedisplacements (in-service movements) of the elements fixed to theanti-seismic device 11 during its life, such as bridges.

For instance, in-service movements in bridges may be caused byvibrations due to heavy loads or by thermal expansion and may lead toparticularly long slip distances during the life of the bridge.

Preferably, a wear test on the sliding material 19 in which the slidingmaterial 19 has a height of at least 2.0 mm from the plane from which itprojects (if it is inserted in an embedded seat) or from the plane onwhich it is applied (if it is not inserted in an embedded seat), withthe application of pressure ranging from 75% to 110% of the designpressure, and at a temperature of 20° C. +8° C. and a velocity of 1 mm/sor more, with a sliding distance of at least 1000 meters, results in thesliding material 19 having its thickness reduced by less than 1.0 mm.

Preferably, subject to the above specification of less than 1.0 mmthickness reduction, the sliding material 19 meets the life test ofEN15129:2009 for use in buildings, even in a variant involving a slidingdistance of more than 1000 m, more preferably a sliding distance of 1600m or more.

Preferably, the sliding material 19 comprises PTFE, more preferably thepolymer material of the sliding material 19 is substantially orexclusively PTFE.

The use of PTFE as a polymer material affords a relatively low frictioncoefficient at low slip velocities.

For instance, in friction tests with slip velocities of less than 10mm/s and with the device 11 loaded with the design load, the frictiondeveloped due to the relative sliding motion of the concave slidingsurface 16 b of the sliding block 16 and the concave sliding surface 17of the upper support 14 is less than 7%.

This allows accommodation of low-velocity in-service movements, aspossibly required by the structure, such as those caused by wind,thermal expansion, sudden load changes on the structure and viscousshrinkage of concrete.

Preferably, a filler, for instance a metal filler, for instance inpowder form is added to PTFE; for example, the filler may be bronzepowder.

Preferably, the metal filler is from 30% to 60%, more preferably from40% to 50% by weight. In a preferred embodiment, the metal filler isabout 45% by weight.

The presence of such amount of metal increases the thermal conductivityof the sliding material 19 as compared with the normal conductivityvalues that can be found in prior art polymer materials.

In the preferred embodiment, in which PTFE is filled with 45% bronzepowder, thermal conductivity is higher than 0.7 W/m*K, and is preferablyabout 0.7 to 0.9 W/m*K.

Preferably, the sliding material is sintered and/or formed into a sheetby compression molding. After molding, the sheet material is processedto the desired thickness.

Preferably, the sliding material 19 as used in the device 11 has athickness of about 8 mm and projects out of the sliding block 16 byabout 3 mm, with about 5 mm thereof being embedded in the sliding block16.

The sliding block 16 of the figures has a sliding block body 16 a, witha seat formed therein for receiving the sliding material 19. The seat isformed on a surface of the sliding block body 16 a which faces towardsthe concave sliding surface 17 of the upper support 14. The slidingblock body 16 a is advantageously made of a metal material, such assteel or an aluminum alloy.

As an alternative configuration, the sliding material 19 may be appliedto the surface of the sliding block 16 in contact with the convexsliding surface 17 of the upper sliding block 14 by adhesives ormechanical fastener means such as screws and/or rivets.

The sliding block body 16 a has a second convex surface 20, facing awayfrom the one on which the sliding material 19 is applied. The surface 20of the sliding block body 16 a preferably has a spherical shape. Thesliding block 16 is rotatably coupled to the lower support 15, therebyforming a ball joint. Particularly, its convex surface 20 is received ina spherical concavity formed in the lower support 15.

Preferably, the surface 20 lies on a layer of sliding material 21, whichis mounted on the lower support 15. Preferably, the sliding material 21consists of a highly-running sheet material, i.e. having a low frictioncoefficient. For instance, the sliding material 21 may be made from anappropriate known polymer material having a friction coefficient of lessthan 7%. This joint material may be suitably lubricated with lubricantsknown in the art, to further reduce its friction coefficient.

Advantageously, in an oscillation test conducted with the sliding block16 and the upper support 14 moving at a relative velocity of about 200mm/s, or about 400 mm/s, with at least 70% of the maximum oscillationamplitude admitted by the device 11 and with a nominal load appliedthereto, after three oscillation cycles the friction coefficient betweenthe concave sliding surface 17 and the convex sliding surface 16 b (i.e.those with the sliding material 19 interposed therebetween) of thedevice 11 is 9% or more, preferably 10% or more.

Advantageously, the sliding material 19 maintains a bearing capacity ofat least 30 MPa when it reaches a temperature of 200° C.

The bearing capacity may be assessed, for instance, by a compressiontest conducted on a 155 m diameter disk of sliding material 19, with themethod described in “Structural Bearings”, by H. Eggert and W. Kauschle,2002, in which such 8 mm thick disk is partially embedded in a metalsupport through 5 mm of its thickness and subjected to constant pressurefor 48 hours.

The bearing capacity is the pressure value at which the deformation ofthe sliding material 19 under load stops within 48 hours and the heightof the disk of sliding material 19 is reduced by less than 2.0 mm.

Alternatively, the assessment may be based on the amount of warping ofthe sliding material 19, which should be, for instance, smaller than 6%,preferably smaller than 4%, e.g. smaller than 2% of its maximum plansize, at the end of the third cycle of the oscillation test as definedabove, when conducted at a velocity of 200 mm/s or at a velocity of 400mm/s.

Furthermore, the sliding material 19 preferably has a softeningtemperature higher than 250° C.

The above clearly shows that the objects of the present invention havebeen fulfilled.

The anti-seismic support can provide earthquake protection to structureslike bridges, which must accommodate considerable in-service slidingmovements even when no earthquake occurs. In fact, the anti-seismicsupport ensures high resistance to the wear caused by mutual slipping ofsliding surfaces.

The anti-seismic support is designed to withstand high-intensity andlong-lasting earthquakes, because the high friction coefficients of thesliding surfaces allows dissipation of a large amount of energy.

The anti-seismic device is reliable over time, even during ahigh-intensity and long-lasting earthquake, as it can adequatelydissipate the thermal energy generated by friction, due to the highthermal conductivity of the sliding material 11, which prevents thetemperature increase at the interface between the convex sliding surface16 b of the sliding block 16 and the concave sliding block 17 of theupper support 14 from causing the sliding surface 11 to soften and thuslead to a considerable reduction of its friction coefficient.

Furthermore, the anti-seismic device has a relatively low friction at alow slip velocity, which allows optimized accommodation of in-servicemovements possibly required by the construction engineering structure.

The sliding material also has a good weather resistance, with verylittle or no moisture absorption.

Those skilled in the art will obviously appreciate that a number ofchanges and variants may be made to the arrangements as describedhereinbefore to meet incidental and specific needs, without departurefrom the scope of the invention, as defined in the following claims.

The preferred embodiment of the invention as disclosed herein is adevice having spherical sliding surfaces, and symmetric with respect toa vertical axis, in operation. Nevertheless it shall be understood that,in a variant, the bearing device might also have cylindrical slidingsurfaces, with a substantially horizontal axis of symmetry, inoperation.

1. An antiseismic device (11) for supporting a civil or constructionengineering structure, said device (11) comprising a first support (14)having a concave sliding surface (17) and a sliding block (16) having aconvex sliding surface (16 d) in sliding contact with said concavesurface (17), wherein said sliding block (16) is capable of sliding withpendulum motion relative to said concave sliding surface (17) inresponse to an earthquake tremor or shock, the device (11) comprising asliding material (19) that forms one of: said concave sliding surface(17) and said convex sliding surface (16 b), wherein the coefficient offriction between said sliding surfaces (16 b, 17) is above 9% when theaverage pressure between said sliding surfaces (16 b, 17) is 30 MPa ormore and the sliding surfaces (16 b, 17) are caused to slide at asliding speed of 50 mm/s or more at a temperature of 20° C. or more,said sliding material (19) comprising a polymeric material filled with apolymeric, synthetic, ceramic or metal filler, wherein if the thesliding material (19) undergoes the test defined by the StandardEN15129:2009, Section 8.3.1.2.5 for antiseismic bearing devices forbuildings or the test defined by the US Standard “AASHTO LRFD BridgeDesign Specification”, Section 15.10.1.2, it exhibits less than 1.0 mmthickness reduction at the end of the test.
 2. A device (11) as claimedin claim 1, wherein said polymeric material is PTFE.
 3. A device (11) asclaimed in claim 1, characterized in that the filler is a metal onlyfiller and comprises bronze.
 4. A device (11) as claimed in claim 3,wherein the metal filler comprises bronze only.
 5. A device (11) asclaimed in claim 1, wherein the metal filler is from 30% to 60% byweight of said sliding material (19).
 6. A device (11) as claimed inclaim 1, wherein the sliding material (19) has a thermal conductivity ofmore than 0.50 W/m*K.
 7. A device (11) as claimed in claim 1, whereinfriction between said sliding surfaces (16 b, 17) is less than 7%, whenthe mutual sliding speed of the sliding surfaces (16, 17) is less than10 mm/s and the contact pressure between the sliding surfaces (16 b, 17)applied to the device (11) is at least 20 MPa.
 8. A device (11) asclaimed in claim 1, wherein in an oscillation test of said device (11)in which the sliding speed between said sliding block (16) and saidfirst support (14) is at least 200 mm/s, the oscillation amplitude is atleast 70% of the maximum admissible oscillation permitted by the device(11) and the nominal load is applied, during the third oscillation cyclethe coefficient of friction between the concave and convex slidingsurfaces (16 b, 17) of the device (11) is 10% or more.
 9. A device (11)as claimed in claim 1, wherein in an oscillation test of said device(11) in which the sliding speed between said sliding block (16) and saidfirst support (14) is at least 400 mm/s, the oscillation amplitude is atleast 70% of the maximum admissible oscillation permitted by the device(11) and the nominal load is applied, during the third oscillation cyclethe coefficient of friction between the concave and convex slidingsurfaces (16 b, 17) of the device (11) is 10% or more.
 10. A device (11)as claimed in claim 1, wherein the sliding material (19) is mounted tothe sliding block (16) either as a sheet partially embedded in acorresponding seat formed on the sliding block (16), or as a sheetapplied using an adhesive or mechanical fastening means and forms theconvex sliding surface (16 b) of the sliding block (16).
 11. A device(11) as claimed in claim 1, wherein the sliding material (19) has asoftening temperature above 250° C.